The diffusivity of macromolecules in the cytoplasm of eukaryotic cells varies over orders of magnitude and dictates the kinetics of cellular processes. However, a general description that associates the Brownian or anomalous nature of intracellular diffusion to the architectural and biochemical properties of the cytoplasm has not been achieved. Here we measure the mobility of individual fluorescent nanoparticles in living mammalian cells to obtain a comprehensive analysis of cytoplasmic diffusion. We identify a correlation between tracer size, its biochemical nature and its mobility. Inert particles with size equal or below 50 nm behave as Brownian particles diffusing in a medium of low viscosity with negligible effects of molecular crowding. Increasing the strength of non-specific interactions of the nanoparticles within the cytoplasm gradually reduces their mobility and leads to subdiffusive behaviour. These experimental observations and the transition from Brownian to subdiffusive motion can be captured in a minimal phenomenological model.

大分子在真核细胞细胞质中的扩散性随数量级而变化，并决定了细胞过程的动力学。然而，尚未实现将细胞内扩散的布朗氏性质或异常性质与细胞质的结构和生化性质相关联的一般描述。在这里，我们测量单个荧光纳米粒子在活的哺乳动物细胞中的迁移率，以获得对细胞质扩散的全面分析。我们确定示踪物的大小，其生化性质和其流动性之间的相关性。大小等于或小于50 nm的惰性粒子的行为就像布朗粒子在低粘度介质中扩散一样，分子拥挤的影响可忽略不计。增加细胞质内纳米颗粒的非特异性相互作用的强度逐渐降低了它们的迁移率并导致了亚扩散行为。这些实验观察结果以及从布朗运动到次扩散运动的转变可以用最小的现象学模型来捕获。